Aviatrix’s recent (and informative) post about alternate minima raises an interesting question: what’s a runway? For example, let’s take a medium-sized airport with a single paved surface, designated 09/27.

Most of us, describing the airport to a friend in the pilot’s lounge, would say that the airport has a single runway 09/27. However, the CAP would publish approach approaches to two different runways, 09 and 27, and the control tower might say “we’re switching the active runway from 09 to 27”. Both runway 09 and 27 will have the same surface type, snow removal, and edge lighting, but they might have different landing and takeoff distances (due to displaced thresholds) and different approach lighting, and most importantly, they’ll be used under different wind conditions. In the middle latitudes of the northern hemisphere, where I live, the wind will generally be from the west in good weather, so runway 27 would be used most often; however, the wind will often be from the east during times of low visibility, so runway 09 is more likely to see instrument approaches in low IMC.

All of this has to do with the Canadian alternate minima Aviatrix mentions in her posting. According to the CAP GEN, you can choose an alternate with forecast 400-1 weather only if there are “two or more usable precision approaches each providing straight-in minima to separate suitable runways.” So if my hypothetical airport had both an ILS 09 and an ILS 27 approach, and the airport were reporting 400 ft ceiling, 1 statute mile visibility, and winds from 180 at 2 knots, would it be a legal alternate? (I grant in advance that flying when your best available alternate is forecast to be 400-1 is pretty questionable regardless) .

Even if 09 and 27 count as two runways, requiring at least two usable straight-in precision approaches gives some insurance: if the wind shifts suddenly to 270@15 knots (but the visibility stays strangely poor), you can still fly the ILS 09. If a small fog bank drifts over the threshold of 09, you can still fly the ILS 27. On the other hand, requiring precision approaches to two separate runway surfaces gives a bit of extra insurance. If someone does a wheels-up landing and closes down 09/27, for example, you can still land on 18/36 (unless, of course, the wheels-up plane came to rest right at the runway intersection).

Because of this second point, it seems that many instructors and examiners have passed on by word of mouth that separate suitable runways means separate suitable runway surfaces — i.e. runway 09/27 and runway 18/36, not runway 09 and runway 27. However, I have not yet succeeded in finding any formal definition, and the AIP and other Canadian publications (not to mention pilots) use the word runway both ways. In real life, this situation is extremely improbable — very few Canadian airports have ILS approaches from both directions to a single runway surface, and those that do are big airports like Toronto/Pearson and Montreal/Trudeau with lots of other precision approaches available.

Still, what’s a runway?